The present invention relates to a pretensioner for straining a belt of a seatbelt system when an emergency occurs. More particularly, the present invention relates to a gas-pressure actuator apparatus used for such a pretensioner.
Vehicles, for example, automobiles, are provided with a seatbelt system which is designed to restrain the occupant's body to the seat. It has been proposed to attach a pretensioner to the seatbelt system as a means for sensing excessive acceleration that acts on the vehicle when an emergency situation, e.g., a collision, occurs, and for straining the belt which has been loosely fastened to the occupant's body, thereby enhancing the restraining effect. The pretensioner is required to perform a reliable action within an extremely short time. Accordingly, there have been proposed a variety of pretensioners which employ a gas-pressure powered direct-acting actuator as a driving source therefor. There has also been a proposal to employ a gas-pressure powered rotary actuator as a driving source for a pretensioner of the type in which a belt take-up shaft of a retractor is rotated.
In the conventional gas-pressure powered rotary actuator, a gas generator that supplies a working gas to the actuator is disposed in a piston rotor of the actuator and arranged to release the generated gas directly into a cylinder chamber through a communicating hole (see Japanese Patent Application Laid-Open (KOKAI) No. 58-195571). Such disposition of the gas generator is considered to be effective in reducing the size of the rotary actuator.
However, in the rotary actuator having the above-described arrangement, the gas that is generated by a reaction (e.g., combustion) in the gas generator is supplied directly into the cylinder chamber through the communicating hole. Accordingly, the gas pressure that is applied to the cylinder chamber is impulsive, and flames of high-temperature gas reach the cylinder chamber. Therefore, there is likelihood that the pretensioner will operate excessively or fail to operate due to excess load or overheating.
Incidentally, one type of inflator for an air bag system adopts an arrangement in which the gas from the gas generator is supplied into the air bag through a hood (functioning as a gas pressure buffer chamber) (see Japanese Patent Application Post-Exam Publication No. 47-15482). With this arrangement, the above-described problems are solved. However, such an arrangement cannot be used for a pretensioner whose installation space is limited in contrast to the air bag system.